RFR: 8297753: AArch64: Add optimized rules for vector compare with zero on NEON [v9]

[Andrew Haley]

On Fri, 3 Mar 2023 07:46:57 GMT, Chang Peng <duke at openjdk.org> wrote:

>> We can use the compare-with-zero instructions like cmgt(zero)[1] immediately to avoid the extra scalar2vector operations.
>> 
>> The following instruction sequence
>> 
>> movi  v16.4s, #0x0
>> cmgt  v16.4s, v17.4s, v16.4s
>> 
>> can be optimized to:
>> 
>> cmgt v16.4s, v17.4s, #0x0
>> 
>> This patch does the following:
>> 1. Add NEON floating-point compare-with-zero instructions.
>> 2. Add optimized match rules to generate the compare-with-zero instructions.
>> 
>> [1]: https://developer.arm.com/documentation/ddi0602/2022-06/SIMD-FP-Instructions/CMGT--zero---Compare-signed-Greater-than-zero--vector--
>
> Chang Peng has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove hard-coded 0b1111 in to_assembler_condition()

Alright! That is _beautiful_.

I felt a bit bad about pushing you  so hard on this, but I think the quality of the result justifies the effort. I hope you agree.

Thank you.

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Marked as reviewed by aph (Reviewer).

PR: https://git.openjdk.org/jdk/pull/11822